1. Field of the Invention
This invention is concerned with a method for the control of ammonia which is being generated by animals.
2. Description of the Previously Published Art
Ammonia is generated quickly in any area in which urine is allowed to collect. This is the result of enzyme-catalyzed hydrolysis of urea, which is a key component of urine. Each molecule of urea may react with water to produce two molecules of ammonia. Ammonia has a disagreeable odor, and may be toxic at high concentrations.
In areas in which animals such as horses, cows, sheep, and pigs are kept, such as stalls, barns, cattle cars, or other enclosures, or in outdoor areas such as feed lots where many animals are maintained in close proximity, considerable amounts of ammonia may accumulate. This is a result of the enzyme-catalyzed hydrolysis of urea in the animal urine, which may collect in significant quantities. As mentioned above, the ammonia possesses an unpleasant smell. Further, ammonia is known to be harmful to animals.
The family of enzymes which catalyze the hydrolysis of urea are known as ureases, here collectively referred to as "urease". In the setting of animal areas, the sources of urease are various bacteria. For example, Proteus mirabilis, found in animal digestive tracts, and Bacillus pasteurii, found in soil, both produce urease. Many types of bacteria may in fact be present. These bacteria need nitrogen for growth and sustenance. As they cannot utilize urea directly to satisfy this need, they produce urease to convert the urea into the usable form of ammonia.
Several methods of lowering the level of ammonia in animal areas are known. The first of these is increased ventilation: by increasing the flow of air into a given space, the average ammonia concentration will be lessened. However, this method may be quite expensive, as it requires power for fans or blowers, as well as entailing increased heating or cooling costs when external air is brought into an enclosed space. Further, in feed lots and similar areas ventilation is impractical.
A second method of controlling the level of ammonia in a given area is through the use of absorbents which are specific for ammonia. However, specific absorbents may be quite expensive. A further concern is that large quantities of absorbents may be required to cope with the ammonia generated in animal areas.
A third method of controlling ammonia accumulation is to prevent its formation. This may be done through the use of biocides to kill the bacteria which produce urease. Biocides which do not harm animals or humans, however, typically will not be effective against all the possible strains of bacteria which may be present. Bacteria also may develop resistance to biocides.
Desiccation also may be used to prevent ammonia formation. When no free liquid is available, little bacterial growth will occur, and hence little urease will be present. In view of the large amounts of urine formed by animals, effective desiccation is very difficult, and will require large quantities of desiccant. Further, these desiccants may be irritating or toxic to animals.
Alternatively, chemicals which prevent catalysis of the hydrolysis of urea by urease may be used. These are known as urease inhibitors. Because each molecule of urease may catalyze the formation of many molecules of ammonia, very small amounts of inhibitor should be needed to prevent the production of noticeable or toxic amounts of ammonia. Thus, it is to be expected that low part-per-million (ppm) levels of inhibitors will be needed.
Finally, chemicals which operate according to more than one of the above mechanisms may be particularly effective. Acids are known to inhibit the growth of urease-producing bacteria. Further, the rate of urease-catalyzed hydrolysis is slowed by a drop in pH. Some acids also may act as inhibitors of urease. For example, it is known that phosphoric acid is an inhibitor of urease; see H. L. T. Mobley and B. P. Hausinger, "Microbial Ureases: Significance, Regulation, and Molecular Characterization", Microbiological Reviews, volume 53, pages 85-108, 1989. Further, any ammonia which is formed may react with acid to form non-volatile ammonium salts.
U.S. Pat. No. 4,306,516 teaches the use of sulfuric acid in a poultry litter. However, the sulfuric acid is present only as an additive to an iron oxide-iron sulfate litter. No use of acid on more common litters as the active ammonia control agent is mentioned.
Canadian Patent 1,191,674 claims the use of a two component additive for litter. The first component is urea phosphate, phosphoric acid, sulfuric acid or an alkali metal bisulfate, and with the second component which is a so-called preservative organic acid or its salts or propane-1,2-diol esters. Relatively large amounts of this mixture can be used, up to 20% of the litter. These amounts will be economical in poultry houses, where litter may be changed annually or less often, but not in, for example, equine operations, where the time between changes of litter is days or weeks. Further, the use of volatile (e.g., acetic), foul-smelling (e.g., isobutyric), and toxic (e.g., acrylic) acids is taught, making the invention less useful in most applications.